Circular dial thermometers are widely used in applications where the thermometer is mounted by means of screw threads and includes a tubular enclosure for supporting a temperature sensor. The tubular enclosure extends into the medium which is to be measured. The temperature, or other parameter, is indicated by the operation of a needle within a circular housing.
Such thermometers as described above have been developed to include a feature for calibrating the temperature reading. The housing is designed to rotate relative to the tube containing the sensor element. The dial of the meter is connected to the housing and the indicator needle is connected to the temperature sensor. Therefore when the housing is rotated relative to the tubular enclosure for the sensor, the dial can be adjusted to be at any point relative to the needle. Thus, after installation, the gauge can be heated to a known temperature such that the housing can then be rotated to place the dial at the correct position relation to the needle. The temperature gauges are typically calibrated at the factory before shipment. Therefore the ultimate calibration at the installation site is minor. However, at the time of installation it is frequently the case that the workman installing the meter uses the housing as a grip for threading the meter into the installation opening. In doing so, especially when the threads become tight, the workman may twist the housing relative to the sensor and needle and this can drastically alter the accuracy of the gauge reading. When such twisting occurs the factory calibration is lost and the gauge must be recalibrated. The recalibration process can be expensive, inconvenient, and time consuming. A bushing is typically joined to the tubular enclosure and is provided with a hex fitting so that the workman can install the gauge without applying any force to the housing. Unfortunately, the bushing is frequently not used.
Therefore there exists a need for a circular gauge which has easy calibration after installation but is not readily subject to miscalibration as a result of incorrect handling of the gauge during installation.